In the field of building construction, a great variety of shoring systems are utilized to facilitate the forming of concrete slabs, beams and other structures. One of the most common implements used in the on-site formation of concrete slabs and beams are hand-set shoring systems. Erecting and dissembling such hand-set shoring systems is a significant part of the normal building construction process whenever elevated concrete slabs or beams are poured on-site. It is therefore desirable to provide an inexpensive shoring system which is readily erected to support such form work in varying job applications, and which is then easily broken down and moved to the next pour site. The size, weight and complexity of a shoring system are all factors which affect the ease with which it is implemented, whereas such factors must be balanced with its strength and durability.
The material of a shoring system is central to most of these considerations. In the past, lumber has been a particularly popular material largely because it tends to be relatively lightweight and inexpensive. Timber supports are also more adaptable than metal supports in the sense that a timber plank can be readily cut, bored or nailed as the particular needs may change from one pour site to the next.
However, the strength and durability of timber supports can be somewhat limiting on their utility, and for that reason many resort to more costly metal supports. Strength and durability are particularly critical for shoring tower legs, which are generally required to carry the substantial majority of the load in a shoring system. Shoring tower legs must also be equipped to interface with the rest of the shoring system. For instance, each leg is typically provided with a screw jack or the like at one or both of its ends to enable adjustment of its length. Couplings, U-heads, and other shoring connections may also be provided at the ends. Because the shoring connections of different systems may have connecting shanks of differing diameters, it is advantageous that a shore leg would be adaptable to receive shanks of differing sizes at the ends thereof.
Because shoring tower legs (or "shore legs") carry principally an axially compressive load, the main structural concern for shoring towers is buckling. The height, diameter, and composition of the leg, factored in relation to the load which it is to carry, are principal determiners in considering its resistance to buckling. The likelihood of buckling is further increased if the load is off-center ("eccentric"). Cross braces and other supports are often used to minimize the risk of buckling. Timber shore legs present several problems in this area because they are more susceptible to splitting than many other materials. The risk of splitting is further increased by the mounting of shoring connections such as screw jacks or braces which tend to create stress concentration where they are mounted to the shore leg.
Laminated veneer lumber ("LVL"), which is essentially lumber formed of thin layers of wood laminated together as a composite, provides an alternative material that is becoming quite popular in the area of formwork supports in general. Some of the benefits of such LVL are that it is straighter and truer than ordinary lumber, it has nearly perfect concentricity of load, and its composite nature enhances its strength while minimizing the weaknesses of flaws in the individual layers. Despite such benefits, though, LVL members are principally used only as secondary supports, such as braces, ledgers or the like when implemented in hand-set shoring systems. One of the problems with using LVL as shoring tower leg material is that, when boring the necessary end bores for mounting screw jacks, U-heads or other connectors in such a solid, strong, and dense material, the drill bit tends to wander off course. The result is a canted end bore which induces what is known as a "dog leg" in the shore, causing bending and reducing its load capacity. Concentric alignment of end bores may be partially ensured with better boring equipment, but the use of such equipment is infeasible at most job-sites. Pre-drilled end bores are a conceivable alternative but their utility is lost when the post is cut to size, thereby eliminating the pre-bored end and defeating its purpose.
Previous products in the field of shoring systems present many examples of the required compromises and limitations accompanying metal shoring. For instance, Cunningham Manufacturing and Formwork Engineering Corp. both have steel beam form systems supported by 5' wide welded steel frames that are load limited and limited to 5' wide.times.10' long towers due to the weight of the steel and the welded structure. The tubular leg naturally accepts the screw jacks and U-heads, but only in a given diameter. The steel cross bracing of those systems is similarly set for several fixed length braces such as 10' that fit 4'-0" stud spacing welded to the legs, with little adaptability of size. Consequently, the shoring towers in such systems cannot fit in certain kinds of structures or under ramps, and the steel beam forms have a limited adjustment range. One of their few advantages is provided by a folding tower which facilitates movement of the system from one pour site to the next.
Other manufacturers supply steel shoring frames somewhat like those described above, with the principal difference being the manner in which braces are attached to the frames. Relatively light-weight aluminum shoring frames are known, although they are not known to be adjustable on-site in width or height, nor are they readily interfaced with other systems, nor do they employ foldable towers.
It is therefore an object of the present invention to enable achievement of high strength with light-weight materials while minimizing the likelihood of buckling in shoring tower legs. Another object of the present invention is to provide a shoring system which utilizes LVL shore legs which can be field cut and provided with virtually concentric end-bores for receiving screw-jacks and other shoring connections therein, thereby ensuring that bending stresses and the risk of premature buckling are minimized.
Many other objects will be obvious from the following summary and description of the invention, particularly when viewed in conjunction with the accompanied drawings and in light of the appended claims.